1. Technical Field
The disclosed embodiments relate in general to a switch circuit, and more particularly to a switch circuit having capacitors and switch elements.
2. Description of the Related Art
Current electronic products, having entered a portable era, are developed towards targets of being compact and low in market prices. However, due to a large number of external components, a volume of a printed circuit board (PCB) is increased to limit a size and an appearance of a product. For example, in most market-available power conversion circuits such as DC/DC converters, charge pump circuits and switched capacitor circuits, elements from power switches, passive elements to control circuits, are all formed by discrete components. Since not only component prices are reducing at a slow and have small margins left for further reduction, but also raw materials are also becoming more costly, assembly costs are increased as the number of employed discrete components grows. Consequently, a PCB becomes larger and heavier.
Further, compared to resistors or ceramic capacitors, magnetic elements have a greater volume and higher costs. Electrolytic capacitors in light-emitting diodes (LED) are prone to interference from the LEDs, and hence have a shortened lifecycle. With a temperature rise of every 10 degree Celsius, the lifecycle of electrolytic capacitors is reduced by 50%. Therefore, there is a need for a driver circuit free of magnetic elements and free of electrolytic capacitors. To effectively reduce the product weight and volume, the integrated circuit technology is a crucial development. Integrated circuits are capable of integrating most external discrete components, e.g., transistors, capacitors and diodes. By replacing a conventional PCB with an integrated circuit having an extremely small volume, the volume and weight can be decreased while also increasing the transmission speed and reliability. However, in addition to high manufacturing costs, an integrated circuit also has a chip area that is directly proportional to costs.
Further, assuming that power switch elements in power conversion circuits are to be integrated to an integrated circuit, a chip area occupied by the power switch elements is quite considerable. In general, a high-power switch element occupies an area of above 5 to 10 times of that of overall control circuits. That is to say, a significant amount of manufacturing costs is consumed if numerous power switch elements are employed in the circuit. Under a condition of generating three to four step-down modes using three capacitors in a conventional switched capacitors, at least eight to nine power switch elements are required and thus render a much too large chip size.